Патент USA US2127564код для вставки
2,127,564 Patented Aug. 23, 1938 UNITED STATES PATENT OFFICE ZINC AMMONiUM CHLORIDE FLUXES Raymond J. Kepfer, Lakewood, Ohio, .assignor, by meme assignments, to E. 1. du Pont de Ne mours 8: Company, Wilmington, DeL, a cor poration of Delaware No Drawing. Application March 5, 1936, Serial No. 67,306 1 Claim. (CL 148-26) This invention relates to zinc ammonium chlo~ ride galvanizing ?uxes, and is particularly direct ed to processes whereinv unsatisfactory zinc am monium chloride galvanizing ?uxes are made 5 suitable for use with foaming agents by reducing the amount of sulfates present as impurities. In hot dip galvanizing, a bath of molten zinc is covered with a ?ux. As articles to be gal vanized are lowered into the molten zinc bath they, 10 of course, first pass thru the ?ux where they are cleaned and prepared for the reception of a metal coating. It has heretofore been the practice to employ foaming agents such as giycerine, tallow, and soap 15 bark with the flux in order to produce a foam or froth. Ordinarily the foaming agent and flux are separately added, as required, to the zinc bath. Sometimes the zinc ammonium chloride flux and foaming agent in predetermined proportions are 20 simultaneously. added to a zinc bath either by adding a mixture of flux and foaming agent‘di rectly to the bath or by adding such a mixture to a pre-wash from which the metal being treated carries the flux and foaming agent to the bath. The foam produced by means of foaming. 25 agents serves to entrap vapors and gases and to retard the rate of volatilization of the flux. For galvanizing operations of this type it is essential that the foam be satisfactory in character and of 30 sufficient thickness. Galvanizers have frequently been confronted with the dii?cuity that, for no apparent reason, it is sometimes extremely difficult or even impossible to obtain a satisfactory foam. Sometimes by 35 using a great excess of foaming agent it was pos sible to obtain a moderately satisfactory foam. In most instances, the diiliculties were surmount ed only by purchasing a new lot of zinc am‘ monium chloride ?ux which would not be so un lieo. satisfactory. I have found» that this hitherto unaccountable behavior on the part of zinc ammonium chloride fluxes is attributable to the presence therein of an excess of sulfate. When sulfates are present in excess of about 2% SO: in zinc ammonium chloride fluxes, it is di?lcult or impossible to produce a satisfactory foam by the use of the customary foaming agents even when such agents are used in very large amounts. Without a satis 50 factory foam on the galvanizing bath, it is, of course, impossible to proceed with the galvanizing operations. It is also observed that when exces sive amounts of sulfates are present in zinc am~ monium chloride ?uxes, there is excessive "fum 55 ing”. That is, the ammonium chloride in the flux :iublin'ies, rapidly destroying the efficacy of the an. Apparently the deleterious sulfates which ren der zinc ammonium chloride ?uxes unusable are inadvertently introduced into the flux in the course of manufacture or they are present be cause the crude materials used are high in sul fates.‘ The sulfates are present, variously, as zinc sulfate, ammonium sulfate, lead sulfate, and evencalcium sulfate. Inasmuch as it is the sul 10 fate radical which is deleterious, I have referred herein to the sulfate content in terms of the per centage of SO: found, in accordance with standard practice. To render usable zinc ammonium chloride ?uxes ‘which contain excessive amounts of sulfates, it is only necessary to remove the sulfates in any de sired manner. I have found it most satisfactory to remove so much of the sulfate as is necessary by adding an acid soluble barium salt, such as 20 barium chloride or barium carbonate, to the flux while it is in dilute solution in the course of its manufacture. The resulting barium sulfate may be removed by decanting or filtering the solution. Strangely enough, barium sulfate does not seem to exercise the deleterious effects experienced with most sulfates unless the barium sulfate is present in amounts exceeding about 5% as S03. If it is desired, therefore, to remove relatively small amounts of sulfate from concentrated zinc " ammonium chloride liquors, the soluble barium salt may simply be added and the resulting barium sulfate included in the product. Of course, if this procedure is followed, great care must be exercised lest too large an amount of barium sulfate be present. if the ?ux and foaming agent are to be added to a galvanizing bath indirectly by using the flux and foaming agent in a pre-dip, the excess of sul fate may be removed by adding a soluble barium salt to the pre-dip. Here again, care must be exercised lest the barium sulfate content be too great. ' Zinc ammonium chloride fluxes superior to those heretofore offered the trade may be prepared by 45 removing substantially all of the sulfate content. If it is not expedient to remove all of the sul fate, zinc ammonium chloride ?uxes of very high quality may be prepared by treating the zinc ammonium chloride ?uxes so that no more than 0 about 0.1% S03 is present. If it is found desirable to remove still less of the sulfate, satisfactory zinc ammonium chloride ?uxes comparable to the best commercial ?uxes heretofore o?ered the trade may be prepared by removing sulfate so that no 55 2 . 2,127,664 more than about 0.2% 80: remains. It is notv preferred,_ however, to leave as much as 0.2% 80: in the flux because with this highest permissible S03 content, it is ordinarily necessary to add a lit-' tle more foaming agent than would be required with the ?uxes having a lower S03 content. The following examples are given more fully to explain the practice of my invention. Example I A commercial zinc ammonium chloride gal vanizing ?ux found unacceptable to the trade was analyzed and was found to contain 1.79% of sulfates computed as S03. This ?ux contained soap bark as a ‘foaming agent. When this flux was tried on a galvanizing bath, a foam formed very quickly, reaching a maximum thickness of about two inches, and subsiding after about four minutes. Using this ?ux, there was excessive 20 fuming. Following the teachings of this inven tion, the sulfates were removed from the flux by adding barium chloride to an aqueous solution thereof. Using the sulfate-free zinc ammonium ' chloride ?ux, a foam blanket about four and a 25 half inches thick was obtained. This foam lasted for about twenty four minutes, and there was very little fuming. Example II Another commercial zinc ammonium chloride 30 ?ux found unacceptable to the trade was analyzed was obtained. Very little fuming was noted with. the improved ?ux composition. Example IV A commercial zinc ammonium chloride flux which contained 1.25% of soap bark as a foaming agent was analyzed and ‘was treated to reduce the sulfate content to about 0.2% computed as S03. The ?ux was much improved, leading to the pro duction of a foam which lasted for about six minutes, and which was about one and one-half inches thick. There was moderate fuming. This ?ux was made more acceptable by increasing the soap bark content to 2.5% after which there was obtained a foam three inches thick which lasted for fourteen minutes. The fuming was consider 15 ably lighter. It will be observed that at the upper limits of sulfate content speci?ed by my inven tion, it is necessary to use a larger amount of foaming agents to produce entirely satisfactory results. The use of an excess of a foaming agent is, of course, expensive and undesirable, and it is generally preferable, therefore, to reduce the sulfate content as much as possible. Example V 25 A concentrated zinc ammonium chloride liquor which contained sulfates equivalent to 0.5% B01 was treated with barium chloride. The zinc am monium chloride was crystallized from the solu tion andqremoved therefrom together with the 30 and was found to contain 0.36% of sulfate com puted as S03. Testing this ?ux on a galvanizing pot, a foam about one inch thick and which barium sulfate. The flux thus produced was used on a galvanizing pot and, after adding foaming 35 lasted for only about two minutes was obtained. tained a foam about two and a half inches thick Considerable fuming of the ?ux was observed, tho it was not quite as bad as the original ?ux mentioned in Example I. Following the procedure of this invention, the sulfates were removed from The flux then led to the production of a foam which lasted for about twenty two minutes and which was about four and a half inches thick. Example III 40 the flux by the use of barium chloride. A zinc ammonium chloride ?ux which was found unacceptable to the trade was analyzed and was found to contain 0.41% of sulfates com puted as S03. This unsatisfactory ?ux produced a foam which lasted for about four minutes and was about one inch thick. This flux contained 0.7% of glycerine as a foaming agent. To re duce the content of sulfates in the flux, there was added thereto a sulfate-free zinc ammonium chloride flux which contained 0.7% of glycerine. The sulfate-free flux was added in an amount sufficient‘ to bring the sulfate content of the mix ture down to 0.05% computed as S03. The re sulting mixture was used as a flux on a galvaniz— 60 ing pot and a foam which lasted for thirteen minutes and which was about four inches thick agents in the customary amount, there was ob which lasted for about fourteen minutes. There was very little fuming. It is thus noted that bari um sulfate equivalent to 0.5% S0: does not exer cise the deleterious effects observed with equally large amounts of other sulfates. If barium sul fate be present in larger amounts, however, it 40 adversely affects the characteristics of the ?ux. While I have shown a number of speci?c pro cedures in the foregoing, it will readily be ap parent that the sulfate content of zinc ammonium chloride ?uxes may be reduced in varying amounts and by various procedures without de parting from the spirit of this invention. I claim: 4.5v In a process for the treatment of a zinc am monium chloride galvanizing ?ux which contains sulfates and hence is unsatisfactory by reason of the poor foam produced when it is used with foaming agents, the flux containing no more than about 0.5% S03, the steps comprising treating the flux with a soluble barium compound to con 55 vert the sulfate to barium sulfate so that when used with foaming agents the ?ux will produce foams of satisfactory thickness and character. RAYMOND J. IQEPFER.